Chemical imaging of latent fingerprints, paint chips, and fibers using µ-FTIR: An experiment for forensic chemistry and instrumental analysis courses

Abstract

Emerging technology combining spectroscopy with microscopy is advancing the analysis of trace evidence with the potential to revolutionize forensic microscopy and excite a new generation of forensic microscopists. In this laboratory experiment, developed for undergraduate forensic chemistry and instrumental analysis courses, students use Fourier transform infrared (micro)spectroscopy (µ-FTIR) to analyze mock forensic samples commonly encountered at crime scenes, including latent fingerprints (laced with ibuprofen to mimic an illicit drug), vehicle paint chips, and acrylic fibers. Unlike light microscopy, µ-FTIR provides information on the spatial distribution and chemical nature of the sample. Learning objectives were to reinforce key concepts covered in the classroom, including collection and preparation of trace evidence, forensic microscopy, and vibrational spectroscopy, as well as to provide students hands-on experience using a state-of-the-art instrument. Students prepared the fingerprint and fiber samples for analysis, whereas the paint chip was previously cross-sectioned to save time. The students collected and processed their own data, including generating chemical distribution maps. Student responses to the exercise were positive and reports written by the students demonstrated an increased awareness of the capabilities of FTIR microscopy and chemical imaging. Overall, the exercise helped remove the “black box” mentality, where students analyze samples without understanding the fundamentals of the technique, which is so important to recognize poor data quality and troubleshoot instruments. This report describes the laboratory exercise and student experience, and includes data and chemical images collected by students, and aspects of the experiment that could be modified to improve learning outcomes.